34 APRIL 2020
are very young or very old, or are unlucky genetically, or have nutritional
deficiencies. Nor, Greenland said, would it “take into account the errors you
always expect in a large-scale system, where there are accidents that put in too
much, and the monitoring is not that good.”
Howard Pollick, an ADA spokesperson and a dental scientist at the
UC San Francisco School of Dentistry, defended water fluoridation in a
recent interview: “The water systems are operated by professionals. With
the new equipment, they can control the fluoride level within a very narrow
range.” As for general safety, he noted, “there’s a 2015 review by the U.S.
Public Health Service that looked at this. I’m comfortable with it.”
Matters get more complex for less well-documented risks. In October,
a research team published the results of a long-term study in Canada that
correlated concentrations of fluoride in the urine of pregnant women with
the IQ scores, three to four years later, of their children. The IQs of the boys
(but not the girls) in fluoridated communities were, roughly speaking, one
to three points lower than those of boys in nonfluoridated communities.
Another long-term study, published in 2017, had found a similar effect in
Mexico (where the fluoride exposure was higher than in Canada). An analy-
sis in 2012 of 27 fluoride-IQ studies from China had also found effects on
cognition (these were retrospective studies, though).
Fluoridation advocates rightly point out that the IQ studies have limi-
tations. However, their position necessarily involves making the gymnas-
tic argument that you should put fluoride in water because its positive
effects have been shown in a bunch of
mostly retrospective studies, but you
should ignore the risk to IQ because the
negative effects have been shown only in
a bunch of mostly retrospective studies.
How should one weigh the potential small
harm to a broad population against the
potential broad benefit to a small popu-
lation? What if neither the harm nor the
benefit is well established? What if con-
straints (moral, financial, logistical) on
our ability to experiment with human
beings mean that these questions can
never be answered definitively?
I asked Anne-Marie Glenny whether
there were other ways of reaching poor
children who can’t go to dentists— training
them to brush their teeth in school, for
instance. Or providing free dental care in
impoverished communities. She said she
was unaware of any research that com-
pared the outcomes of fluoridation with
these alternatives.
Given all the uncertainties, I asked,
can we really say that fluoridation works?
“There’s no argument that fluoridation
doesn’t work,” Glenny said. “The question is
whether it is still the right way forward.”Charles C. Mann is a contributing writer at
The Atlantic. His books include The Wizard
and the Prophet (2018) and 1491 (2005).The dental establishment’s argument for
fluoridating water in a society where a majority of
people use fluoridated toothpaste and go to the dentist
boils down to a contention that fluoridation will likely
help people who are unable to afford good dental care.
The idea is that poor children don’t brush their teeth,
and fluoridation will fill the gap—a notion, inciden-
tally, that the Cochrane team found no good evidence
to support. (Last year, JAMA Pediatrics published a
large, careful study that suggested fluoridation gave
extra benefit to poor children and adolescents, but it,
too, had limitations—the authors could not establish
whether the different families in the study ate similar
amounts of sugar, for instance.) Still, the argument
runs, it is ethically acceptable to force a majority to
do something potentially useless if it might benefit a
minority. Unless, of course, fluoridation at current
levels is unsafe in some way, and the many are harmed
in pursuit of a potential benefit for the few.
Is it safe? Some fluoride perils are well documented.
Over the long run, the body incorporates fluoride
into bone, making it more prone to fracture, and into
ligaments and joints, making them less flexible and
sometimes making movement very painful.
Severe cases of fluorosis are crippling; most
victims are elderly. As a result, fluoridation
advocates and people in government must
thread a needle: enough fluoride to pro-
tect against tooth decay in children, but not
enough to cause problems in the long term.
Alas, epidemiologists have been com-
plaining about the safety studies for decades,
according to Sander Greenland, an emeritus
professor of epidemiology and statistics at
UCLA. Greenland, who is a co-author of
the standard textbook Modern Epidemiol-
ogy, began his own fluoridation work in the
’70s by examining a “typical crap ecologi-
cal study” supposedly showing that fluoride
caused cancer. “But then I got into the litera-
ture, just because I wanted to do a thorough
job, and I noticed there was really no safety
information. They didn’t have any good
rationale for the dose.” The current U.S.
recommendation is 0.7 milli grams per liter.
Greenland went on: “Since they didn’t
have any good long-term data, the precau-
tionary approach would be ‘What’s the
smallest amount we can put in [so that]
we get most of the benefit and minimize
the likelihood of long-term harm?’ Instead,
that mentality was totally absent from the
literature.” Moreover, a seemingly prudent
level doesn’t account for the possibility
that certain people may be extra-sensitive
to fluo ride’s negative effects, because they